Seven animal rights extremists who subjected scores of victims to a "climate of fear" have been convicted of co-ordinating a six-year campaign of blackmail and menaces to shut down Huntingdon Life Sciences.

The three women and four men were found guilty after a two-year, £3.5 million police investigation into Stop Huntingdon Animal Cruelty, an international campaign to close down the Cambridgeshire-based animal research laboratory.

Prosecutors believe that among these members of SHAC's hierarchy were some of the key figures in the Animal Liberation Front, the often violent movement that acts as an umbrella for much animal rights extremism worldwide.

Two of SHAC's founding members, Gregg Avery, 41, and his wife Natasha, 39, along with fellow activist Daniel Amos, 22, pleaded guilty earlier this year to conspiracy to blackmail.

Today, following a three-month trial at Winchester Crown Court, Avery's former wife and fellow SHAC founder Heather Nicholson, 41, was found guilty of the same offence.

Three further conspirators, Daniel Wadham, 21, Gerrah Selby, 20 and Gavin Medd-Hall, 45 were also convicted. All are expected to be sentenced next month. The maximum sentence for conspiracy to blackmail is 14 years imprisonment. An eighth defendant, 51-year-old Trevor Holmes from Newcastle, was acquitted.

Sentencing will take place on January 19 at Winchester Crown Court. Selby, Wadham and Medd-Hall were released on conditional bail, while Nicholson was remanded in custody.

Detective Chief Inspector Andy Robbins from Kent Police, who led the investigation, said: "This conspiracy to blackmail involved the systematic and relentless intimidation of individuals and their companies. The conspiracy ran for six years, until it was stopped by the arrests.

"The public should be aware that money donated in good faith to Stop Huntingdon Animal Cruelty (SHAC) was in fact being used to finance this criminal conduct."

"The ALF is simply a name given to criminal behaviour," he said. "There’s no club and no rules of membership."

SHAC's victims received threatening letters, hoax bombs and sanitary towels allegedly contaminated with the HIV virus, while their neighbours were sent anonymous letters warning them that they lived close to a paedophile.

The managing director of one targeted company received a letter in December 2006 that threatened: "We will attack your property, your family or you, whichever we see fit . . . The screams of the animals are in our heads. We will not fail them. You will pay for their agony."

The targets, who worked for companies that did business directly or indirectly with HLS, were usually targeted after they were listed as 'collaborators' on SHAC's website.

This persecution, often of people who were only loosely connected with animal research, normally stopped only when a victim's company agreed to sever its links with the laboratory.

Avery and the rest of his core group denied any links to the ALF or the blackmailing of HLS "collaborators" whose details appeared on SHAC's website.

However, Michael Bowes QC, for the prosecution, told the court that although the "darker" part of the campaign was labelled ALF, those attacks were "are all part and parcel of the conspiracy".

"In relation to these activities and these extremists or we would say criminal activists, SHAC and the ALF are one and the same...Because of course there is no club or organisation that you sign up for with a membership card or rules and a structure of the ALF. It is a badge, a name, given to a type of behaviour."

Operation Achilles, a two-year investigation that included bugging SHAC's Hampshire headquarters, culminated in the arrests of 32 people in a series of raids involving 700 police officers across Britain and in Belgium and Holland last May.

Four other people have already been convicted as a result of the operation, including Philip Malkin, who sent threatening e-mails in the name of SHAC Leeds to companies on the SHAC target list, and Diane Jamieson, a 64-year-old who sent anonymous threatening letters to numerous companies and individuals, signed off as the ALF.

Both were convicted of interfering with the contractual relationships of an animal research organisation. Suzanne Jaggers was sentenced to nine months in prison for blackmail at Leeds Crown Court, while Graham Berry pleaded guilty at to theft of a document.

Many of criminal acts perpetrated by SHAC were funded directly or indirectly by collections from the public on the high streets of Britain.

One stall on Oxford Street, Central London, could make £500 in a single day while thousands of people signed petitions that were never presented to anyone. Boxes full of completed petition sheets were discovered last May in a police raid on a cottage at Little Moorcote in Hampshire from where SHAC was run with what was called almost military precision.

Nearly £100,000 in cash was found there and at the other 29 addresses raided by police. The cash was a small portion of global donations totalling around £1 million.

Alastair Nisbet, a Crown Prosecution Service lawyer, congratulated the victims who dared to come forward to testify against SHAC. "Some of those victims have, with considerable courage, come to court to give very moving evidence of their experiences," he said outside court.

A spokesman for HLS said: "Freedom of expression and lawful protest are important rights in our democratic society but so too is the right to conduct vital biomedical research, or to support organisations that perform such research, without being harassed and threatened.

"HLS is proud to play its role in helping to develop safe and effective new medicines that can make a real difference to people’s lives."

Cecilia, Windsor, well said. We have become used to the idea of animals as 'things' to be exploited as and when it supposedly benefits us, that many don't see it as wrong any more. Doesn't mean it's right.

maggie, London , uk

The law would prohibit me from performing painful experiments on my pets at home so why is it allowed behind closed doors. Torture is torture wherever the location